It is highly desirable for rubbery polymers that are used in manufacturing tires, hoses, power transmission belts and other industrial products to have good compatibility with fillers, such as rubber reinforcing carbon black and amorphous rubber reinforcing silica. In cases where other materials, such as clay or starch, are used as reinforcing fillers for the rubber, it is also beneficial for the rubbery polymer to have good compatibility therewith. To attain improved interaction with fillers, such rubbery polymers can be functionalized with various compounds such as amines. For instance, U.S. Pat. No. 4,935,471 discloses a process for preparing a polydiene having a high level of affinity for carbon black which comprises reacting a metal terminated polydiene with a capping agent selected from the group consisting of (a) halogenated nitrites having the structural formula X-A-C≡N, wherein X represents a halogen atom and wherein A represents an alkylene group containing from 1 to 20 carbon atoms, (b) heterocyclic aromatic nitrogen containing compounds, and (c) alkyl benzoates.
The capping agents disclosed by U.S. Pat. No. 4,935,471 react with metal terminated polydienes and replace the metal with a terminal cyanide group, a heterocyclic aromatic nitrogen containing group or a terminal group which is derived from an alkyl benzoate. For example, if the metal terminated polydiene is capped with a nitrile, it will result in the polydiene chains being terminated with cyanide groups. The use of heterocyclic aromatic nitrogen containing compounds as capping agents can result in the polydiene chains being terminated with a pyrrolyl group, an imidazolyl group, a pyrazolyl group, a pyridyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an indolizinyl group, an isoindolyl group, a 3-H-indolyl group, a cinnolinyl group, a pteridinyl group, a β-carbolinyl group, a perimidinyl group, a phenanthrolinyl group or the like.
U.S. Pat. No. 4,935,471 also discloses that lithium amides are highly preferred initiators because they can be used to prepare polydienes which are terminated with polar groups at both ends of their polymer chains. The extra polar functionality provided by lithium amides results in increased interaction with carbon black resulting in better polymer-carbon black dispersion. The lithium amides disclosed by U.S. Pat. No. 4,935,471 include lithium pyrrolidide. U.S. Pat. No. 4,935,471 also indicates that preferred initiators include amino alkyl lithium compounds of the structural formula:
wherein A represents an alkylene group containing from 1 to 20 carbon atoms, and wherein R1 and R2 can be the same or different and represent alkyl groups containing from 1 to 20 carbon atoms.
It is also desirable for synthetic rubbers to exhibit low levels of hysteresis. This is particularly important in the case of rubbers that are used in tire tread compounds. Such polymers are normally compounded with sulfur, carbon black, accelerators, antidegradants and other desired rubber chemicals and are then subsequently vulcanized or cured into the form of a useful article. It has been established that the physical properties of such cured rubbers depend upon the degree to which the carbon black is homogeneously dispersed throughout the polydiene rubber. This is in turn related to the level of affinity that carbon black has for the rubber. This can be of practical importance in improving the physical characteristics of rubber articles that are made utilizing polydiene rubbers. For example, the rolling resistance and tread wear characteristics of tires can be improved by increasing the affinity of carbon black to the rubbery polymers utilized therein. Therefore, it would be highly desirable to improve the affinity of a given polydiene rubber for carbon black and/or silica. This is because a better dispersion of carbon black throughout polydiene rubbers which are utilized in compounding tire tread compositions results in a lower hysteresis value and consequently tires made therefrom have lower rolling resistance. It is also known that a major source of hysteresis is due to polymer chain ends that are not capable of full elastic recovery. Accordingly, improving the affinity of the rubber chain ends to the filler is extremely important in reducing hysteresis.
U.S. Pat. No. 6,080,835 discloses a functionalized elastomer comprising: a functional group defined by the formula:
where R1 is a selected from the group consisting of a divalent alkylene group, an oxy-alkylene group, an amino alkylene group, and a substituted alkylene group, each group having from about 6 to about 20 carbon atoms, R2 is covalently bonded to the elastomer and is selected from the group consisting of a linear-alkylene group, a branched-alkylene group, and a cyclo-alkylene group, each group having from about 2 to about 20 carbon atoms.
U.S. Pat. No. 5,932,662 discloses a method of preparing a polymer comprising: polymerizing one or more anionically polymerizable monomers in a solvent in the presence of a polymerization initiator of the formula:
wherein R1 is a divalent alkylene, an oxy- or amino-alkylene having from 6 to about 20 carbon atoms, wherein R2 is a linear-alkylene, branched-alkylene, or cyclo-alkylene having from about 2 to about 20 carbon atoms, wherein Li is a lithium atom bonded directly to a carbon atom of R2; and wherein R3 is a tertiary amino, an alkyl having from about 1 to about 12 carbon atoms, an aryl having from about 6 to about 20 carbon atoms, an alkaryl having from about 7 to about 20 carbon atoms, an alkenyl having from about 2 to about 12 carbon atoms, a cycloalkyl having from about 5 to about 20 carbon atoms, a cycloalkenyl having from about 5 to about 20 carbon atoms, a bicycloalkyl having from about 6 to about 20 carbon atoms, and, a bicycloalkenyl having from about 6 to about 20 carbon atoms, and where n represents an integer of from 0 to about 10.
U.S. Pat. No. 6,084,025 discloses a functionalized polymer prepared by a process comprising the steps of: preparing a solution of a cyclic amine compound, an organolithium compound, and from 3 to about 300 equivalents, based upon one equivalent of lithium, of a monomer selected from vinyl aromatic monomers, and mixtures thereof, where said cyclic amine compound is defined by the formula:
where R2 is selected from the group consisting of an alkylene, substituted alkylene, bicycloalkane, and oxy-alkylene group or N-alkylamino-alkylene group having from about 3 to about 16 methylene groups, wherein N represents a nitrogen atom, and wherein H represents a hydrogen atom, thereby forming a polymerization initiator having the formula A(SOL)yLi, where Li is a lithium atom, SOL is a divalent hydrocarbon group having from 3 to about 300 polymerized monomeric units, y is from 0.5 to about 3, and A is a cyclic amine radical derived from said cyclic amine; charging the solution containing A(SOL)yLi with from about 0.01 to about 2 equivalents per equivalent of lithium of a chelating reagent, and an organic alkali metal compound selected from compounds having the formula R4OM, R5C(O)OM, R6R7NM, and R8SO3M, where R4, R5, R6, R7, and R8 are each selected from alkyls, cycloalkyls, alkenyls, aryls, or phenyls, having from 1 to about 12 carbon atoms; and where M is Na, K, Rb or Cs, and sufficient monomer to form a living polymeric structure; and quenching the living polymeric structure.
In the initiator systems of U.S. Pat. No. 6,084,025 a chelating reagent can be employed to help prevent heterogeneous polymerization. The reagents that are reported as being useful include tetramethylethylenediamine (TMEDA), oxolanyl cyclic acetals, and cyclic oligomeric oxolanyl alkanes. The oligomeric oxolanyl alkanes may be represented by the structural formula:
wherein R9 and R10 independently are hydrogen or an alkyl group and the total number of carbon atoms in —CR9R10— ranges between one and nine inclusive; wherein y is an integer of 1 to 5 inclusive; wherein y′ is an integer of 3 to 5 inclusive, and wherein R11, R12, R13, and R14 are independently —H or —CnH2n+1, and wherein n represents an integer within the range of 1 to 6.
U.S. Pat. No. 6,344,538 discloses functionalized monomers and polymerized functionalized monomers selected from the group consisting of 2-(N,N-dimethylaminomethyl)-1,3-butadiene, 2-(N,N-diethylaminomethyl)-1,3-butadiene, 2-(N,N-di-n-propylaminomethyl)-1,3-butadiene, 2-(cyanomethyl)-1,3-butadiene, 2-(aminomethyl)-1,3-butadiene, 2-(hydroxymethyl)-1,3-butadiene, 2-(carboxymethy)-1,3-butadiene, 2-(acetoxymethyl)-1,3-butadiene, 2-(2-alkoxy-2-oxoethyl)-1,3-butadiene, 2,3-bis(cyanomethyl)-1,3-butadiene, 2,3-bis(dialkylaminomethyl)-1,3-butadiene, 2,3-bis(4-ethoxy-4-4-oxobutyl)-1,3-butadiene and 2,3-bis(3-cyanopropyl)-1,3-butadiene, and methods for preparing such functionalized diene monomers and polymers.
U.S. Pat. Nos. 6,627,721, 6,630,552, 6,664,328, 6,790,921, 6,812,307, and 6,927,269 relate to rubbery polymers having functionality for better interaction with fillers incorporated therein through the use of functionalized vinyl aromatic monomers. For instance, U.S. Pat. No. 6,812,307 discloses rubbery polymers that contain functionalized monomers of the structural formula:
wherein n represents an integer from 4 to about 10, into rubbery polymers.
U.S. Pat. Nos. 6,627,721 and 6,630,552 disclose rubbery polymers that are comprised of repeat units that are derived from (1) at least one conjugated diolefin monomer, and (2) at least one functionalized monomer having of the structural formula:
wherein R represents an alkyl group containing from 1 to about 10 carbon atoms or a hydrogen atom, and wherein R1 and R2 can be the same or different and represent hydrogen atoms or a moiety selected from the group consisting of
wherein R3 groups can be the same or different and represent alkyl groups containing from 1 to about 10 carbon atoms, aryl groups, allyl groups, and alkyloxy groups of the structural formula —(CH2)y—O—(CH2)z—CH3, wherein Z represents a nitrogen containing heterocyclic compound, wherein R4 represents a member selected from the group consisting of alkyl groups containing from 1 to about 10 carbon atoms, aryl groups, and allyl groups, and wherein n, x, y and z represents integers from 1 to about 10, with the proviso that R1 and R2 can not both be hydrogen atoms.
U.S. Pat. Nos. 6,825,306, 6,901,982, and 7,041,761 disclose a rubbery polymer having improved compatibility with fillers which is comprised of repeat units that are derived from (1) at least one conjugated diolefin monomer, and (2) at least one functionalized monomer of the structural formula:
wherein the R′ groups in repeat units and in different repeat units can be the same or different and represent hydrogen atoms or alkyl groups containing from 1 to about 4 carbon atoms, wherein x represents an integer from 1 to about 10, and wherein the R groups in repeat units and in different repeat units can be the same or different and represent alkyl groups containing from 1 to about 10 carbon atoms or alkoxy groups containing from 1 to about 10 carbon atoms.
U.S. Pat. Nos. 6,693,160, 6,753,447, 6,933,358, and 6,936,669 also disclose the use of monomers that can be incorporated into rubbery polymers to improve compatibility with fillers. These polymers include those that are of the structural formula:
wherein R and R′ can be the same or different and represent allyl, alkoxyl or alkyl groups containing from 1 to about 10 carbon atoms, and
wherein m represents an integer from about 4 to about 10.
U.S. Pat. No. 6,369,167 B1 discloses a modified diene polymer capable of creating good reinforcing characteristics and filler dispersing effect independently of the kinds of the filler as well as a process for making the polymer and to provide a rubber composition having good fracture characteristics, wear resistance, and low exothermicity without the impairment of wet performance. The above-described object can be achieved by a process for making the polymer, said process comprising the steps of polymerizing or copolymerizing a conjugated diene monomer by using an organolithium compound as an initiator in a hydrocarbon solvent and thereafter allowing the active termination of the polymer to react with a compound having an alkylideneamino group represented by the formula:
wherein R, R′, R″, and R′″ each represent a group having 1 to 18 carbon atoms selected from the group consisting of: an alkyl group, an allyl group, or an aryl group; and m and n are integers of from 1 to 20 and from 1 to 3, respectively.